Computers, fax machines, printers and other electronic devices are routinely connected by communications cables to network equipment such as routers, switches, servers and the like. FIG. 1 illustrates the manner in which a computer 10 may be connected to network equipment 20 using conventional communications plug/jack connections. As shown in FIG. 1, the computer 10 is connected by a patch cord 11 to a communications jack 30 that is mounted in a wall plate 18. The patch cord 11 comprises a communications cable 12 that contains a plurality of individual conductors (e.g., insulated copper wires) and first and second communications plugs 13, 14 that are attached to the respective ends of the cable 12. The first communications plug 13 is inserted into a communications jack that is provided in the computer 10 (this jack is not visible in FIG. 1), and the second communications plug 14 is inserted into a plug aperture 32 in the front side of the communications jack 30. The contacts or “blades” of the second communications plug 14 are exposed through the slots 15 on the top and front surfaces of the second communications plug 14 and mate with respective contacts of the communications jack 30. The blades of the first communications plug 13 similarly mate with respective contacts of the communications jack that is provided in the computer 10.
The communications jack 30 includes a back-end wire connection assembly 34 that receives and holds conductors from a cable 36. As shown in FIG. 1, each conductor of cable 36 is individually pressed into a respective one of a plurality of slots provided in the back-end wire connection assembly 34 to establish mechanical and electrical connection between each conductor of cable 36 and a respective one of a plurality of conductive paths (not shown in FIG. 1) through the communications jack 30. The other end of each conductor in cable 36 may be connected to, for example, the network equipment 20. The wall plate 18 is typically mounted on a wall (not shown) of a room or office of, for example, an office building, and the cable 36 typically runs through conduits in the walls and/or ceilings of the building to a room in which the network equipment 20 is located. The patch cord 11, the communications jack 30 and the cable 36 provide a plurality of signal transmission paths over which information signals may be communicated between the computer 10 and the network equipment 20. It will be appreciated that typically one or more patch panels, along with additional communications cabling, would be included in the electrical path between the cable 36 and the network equipment 20. However, for ease of description, in FIG. 1 the cable 36 is shown as being directly connected to the network equipment 20.
In the above-described communications system, the information signals that are transmitted between the computer 10 and the network equipment 20 are typically transmitted over a pair of conductors (hereinafter a “differential pair” or simply a “pair”) rather than over a single conductor. An information signal is transmitted over a differential pair by transmitting signals on each conductor of the pair that have equal magnitudes, but opposite phases, where the signals transmitted on the two conductors of the pair are selected such that the information signal is the voltage difference between the two transmitted signals. The use of differential signaling can greatly reduce the impact of noise on an information signal.
Various industry standards, such as the TIA/EIA-568-B.2-1 standard approved Jun. 20, 2002 by the Telecommunications Industry Association, have been promulgated that specify configurations, interfaces, performance levels and the like that help ensure that jacks, plugs, cables and the like that are produced by different companies will all work together. The most commonly followed of these industry standards specify that each jack, plug and cable segment in a communications system must include a total of eight conductors 1-8 that are arranged as four differential pairs of conductors. The industry standards specify that, in at least the connection region where the contacts (blades) of a plug mate with the contacts of the jack (referred to herein as the “plug-jack mating region”), the eight conductors are generally aligned in a row. As shown in FIG. 2, under the TIA/EIA 568 type B configuration, conductors 4 and 5 in FIG. 2 comprise differential pair 1, conductors 1 and 2 comprise differential pair 2, conductors 3 and 6 comprise differential pair 3, and conductors 7 and 8 comprise differential pair 4. Conductors 1, 3, 5 and 7 are referred to as “tip” conductors, and conductors 2, 4, 6 and 8 are referred to as “ring” conductors.
Unfortunately, the industry-standardized connector configuration shown in FIG. 2, which was adopted many years ago, generates a type of noise known as “crosstalk.” As is known to those of skill in this art, “crosstalk” refers to unwanted signal energy that is induced onto the conductors of a first “victim” differential pair from a signal that is transmitted over a second “disturbing” differential pair. The induced crosstalk may include both near-end crosstalk (NEXT), which is the crosstalk measured at an input location corresponding to a source at the same location (i.e., crosstalk whose induced voltage signal travels in an opposite direction to that of an originating, disturbing signal in a different path), and far-end crosstalk (FEXT), which is the crosstalk measured at the output location corresponding to a source at the input location (i.e., crosstalk whose signal travels in the same direction as the disturbing signal in the different path). Both types of crosstalk degrade the information signal on the victim differential pair.
Various techniques have been developed for cancelling out the crosstalk that arises in industry standardized plugs and jacks. Many of these techniques involve including crosstalk compensation circuits in each communications jack that introduce “compensating” crosstalk that cancels out much of the “offending” crosstalk that is introduced in the plug and the plug-jack mating region due to industry-standardized plug-jack interface. In order to achieve high levels of crosstalk cancellation, the industry standards have for many years required that each communication plug introduce defined levels of crosstalk between the four differential pairs, which allows each manufacturer to design the crosstalk compensation circuits in their communications jacks to cancel out these predefined amounts of crosstalk. Typically, the communications jacks use “multi-stage” crosstalk compensation circuits as disclosed, for example, in U.S. Pat. No. 5,997,358 to Adriaenssens et al. (hereinafter “the '358 patent”), as these multi-stage crosstalk compensating schemes can provide significantly improved crosstalk cancellation, particularly at higher frequencies. The entire contents of the '358 patent are hereby incorporated herein by reference as if set forth fully herein.